The present invention relates to a raster operation circuit which displays a figure, the display color of which changes for each pixel, on a rectangular region of a screen.
A graphic display apparatus having a frame memory for storing a figure to be displayed normally processes figures as a set of lines. In recent years, such a graphic display apparatus is required to display a figure, the display color of which changes for each pixel like a photograph, i.e., to perform a raster operation. The raster operation is conventionally performed by address conversion and display color designation processing for each pixel by a microprocessor, and the like.
However, the conventional raster operation applies a heavy load to the microprocessor, and takes a great deal of processing time. In addition, the graphic display apparatus of this type is required to display a figure, in which an arbitrary number of continuous pixels are displayed in an identical color, i.e., to perform a run-length operation. The run-length operation is conventionally performed by address conversion and display color designation processing for each pixel by a microprocessor, and the like.
However, the run-length operation similarly applies a heavy load to the microprocessor, and takes a great deal of processing time.